Intra Operative Neuro Monitoring (IONM) Flashcards
How is an electroencephalogram (EEG) used for intraoperative monitoring and diagnosis?
- monitors CNS function and ischemia
- burst suppression
- depth of anesthesia
What happen to the EEG waves during ischemia?
A progressive reduction in CBF will produce a reliable pattern change in the EEG
- loss of high frequency activity
- loss of power
- eventual progression to EEG silence
What is cerebral oximetry?
Noninvasive cerebral oxygenation measurement using near infrared spectroscopy (NIRS) technology
When is cerebral oximetry used?
Any procedure where there may be vascular compromise to the brain from restriction of blood flow or patient positioning
During cerebral oximetry, what measurement is significant?
A decrease of 20% from baseline
In conjunction with standard monitors, what other monitor is used to measure depth of anesthesia?
The BIS monitor
What do 0, 20,40,60 80 and 100 represent on a BIS monitor?
0 = flatline EEG
0-20 = burst suppression
20-40= deep hypnotic state
40-60 = general anesthesia
- low probability of explicit recall.
- unresponsive to verbal stimulus
60-80 = responds to loud command or mild prodding/shaking
80-100 = awake- responds to normal voiceWhat do evoked potential modalities detect?
Signals that are the results of specific stimuli applied to the patient
What are the different types of evoked potentials?
Somatosensory evoked potential SSEP
Brainstem auditory evoked potential BAEP
Visual evoked potential. VEP
Motor evoked potential. MEP
What is the proposed benefit of EP monitoring?
To identify the deterioration of neuronal function in order to provide opportunity to correct offending factors before they are irreversible.
During EP monitoring, what are potential offending factors?
- position of the patient
- hypotension
- hypothermia
- surgical intervention
What is an SSEP?
- A signal that is detectable on EEG monitoring the primary somatosensory cortex
- generated by a cutaneous electrical stimulation of a peripheral sensory nerve or a cranial nerve with a sensory pathway
How is SSEP described?
Described by:
- Polarity: direction of wave deflection
- latency: time required for a signal to be detected after a stimulus has been applied
What is an SSEP quantified by?
Quantified by:
- amplitude of the resulting signal
- latency of the resulting signal
During SSEP monitoring, _________ _________ is more common than mechanical disruptive change.
Ischemic change
During SSEP, ischemia causes ____________ of the signal to decrease and the ___________ of the signal to increase.
Amplitude
Latency
What are clinically significant SSEP wave changes?
- 50% decrease in signal amplitude
- 10% increase in signal latency
How is Motor evoke potential (MEP) different from other EP modalities?
It evaluates descending motor pathways
_____ acts as a complement to SSEP, particularly in the setting of _______ _________.
MEP
Spine surgery
What does using both SSEP and MEP monitoring during spine surgery provide?
Information about the integrity of anatomically different areas of the spinal cord.
What happens to elicit an MEP?
- A stimulus is applied in a transcranial fashion over the motor cortex
- the deflection, essentially an electomyographic signal, is then detected by electrodes embedded in the muscle belly
Transcranial electrical stimulus is usually delivered as a _____ ___________________, the voltage is then adjusted to achieve adequate signals in both the ________ and _______ extremities.
Rapid train of four or more stimuli
Upper
Lower
Which agents have more depressant effects on EP monitoring?
Inhalation agents, including nitrous oxide generally have more depressant effects than IV agents
T/F volatile agents can have a profound influence on the amplitude and latency of evoked potentials.
True
EP signals can be obtainable under volatile anesthesia. How is this achieved?
Keeping the anesthetic at sub-MAC doses to avoid degradation in quality of the signals
What do Propofol and Thiopental do to EPs?
Attenuate the amplitude of all modalities of EP, but do not obliterate them
What do ketamine and Etomidate do to SSEPs?
Enhance the quality of SSEP signals in patients with a weak baseline, although clinical significance remains unclear
What effects to opioids, benzos, and precedex have on EPs?
Negligible effects on recording of EP
MEP are exquisitely sensitive to the ___________ effects of _______ ________, including nitrous oxide.
Depressant
Inhalation anesthetics
What is the ideal anesthesia for monitoring MEP?
TIVA without nitrous oxide
Monitoring of MEP generally precludes the use of ____________.
Paralytics
MEP can cause ______ __________, so MEP signals are typically obtained intermittently at points during surgery.
Patient movement
What is mandatory to prevent injury to the tongue during transcranial stimulation?
A bite block
